A stent is a medical device adapted for propping open an obstructed passage within the body, such as a blocked ureter. In general, ureteral blockage is a medical condition requiring treatment. A ureteral blockage can occur for a number of reasons, including the passage of a kidney stone and/or other material into the ureter where it becomes entrapped. Also, a tumor growing against the outer wall of the ureter can force compression or constriction of the ureter. A tumor on the internal ureteral wall can also cause blockage of the ureter. Ureteral stents are often used to correct such problems. A ureteral stent may be placed inside the ureter on a temporary basis to allow proper drainage of fluids from the kidney to the urinary bladder. One end of a typical ureteral stent is placed in the kidney and the other end is placed in the urinary bladder. The end positioned in the kidney is typically configured to retain the stent within the renal pelvis and to prevent the downward migration of the stent into the ureter. The bladder end of the stent is typically configured to prevent upward migration of the stent towards the kidney.
FIG. 1 is a conceptual background drawing showing a portion of the human urinary tract. Referring to FIG. 1, in a human urinary tract 100, the ureters 102 and 104 transport urine from the kidneys 106 and 108 to the urinary bladder 110. The trigone region 112 of the urinary bladder 110 is located between the urethral opening 114 and the two ureteral orifices 116 and 118. The pain associated with an in-dwelling ureteral stent is attributable in-part to contact between the stent and the urinary bladder mucosa 120 in the trigone region 112. The trigone region 112 is believed to be particularly innervated and sensitive to the presence of any foreign bodies such as the bladder end of a ureteral stent.
The placement of conventional ureteral stents generally requires a measurement by the physician to ascertain the length of, for example, the ureter 102. Typically, conventional stents include an elongate body at least long enough to traverse the distance in the ureter 102 between the kidney 106 and the urinary bladder 110. Conventional stents also typically include some type of anchor at one or both of the kidney 106 and urinary bladder 116 ends. Such anchors generally consist of a coil formed perpendicular to a stent axis and integrated with one or both of the kidney 106 and urinary bladder 110 ends of the stent. These coils secure the stent to prevent it from migrating in the ureter 102, either upward toward the kidney 106 or downward toward the urinary bladder 110.
One drawback of such conventional stents, is that typically, they need to be of sufficient length to allow for some relative movement between the kidney 106 and the urinary bladder 110, due to, for example, patient movement or peristaltic action, without becoming dislodged. However, such increased stent length can cause the stent to protrude far enough into the kidney 106 and/or the urinary bladder 110 to cause kidney 106 and urinary bladder 110 irritation. The trigone region 112 of the urinary bladder 110 is especially susceptible to such irritation. To further complicate matters, stents having insufficient length may dislodge and migrate in the ureter 102, either toward the kidney 106 or toward the urinary bladder 110.